1. Field of the Invention
The present invention relates to an exhaust throttle valve diagnosing device and method for diagnosing mechanical failure of an exhaust throttle valve provided in an exhaust passage of an engine.
2. Description of the Related Art
Exhaust throttle valves for throttling the exhaust of an exhaust passage are fitted to, for example, the diesel engines of large automotive vehicles (see, for example, Japanese Unexamined Patent Application No. H11-148375).
Such exhaust throttle valves are controlled to throttle the exhaust when, for example, engine warm-up and exhaust purifying filter device (DPD device) regeneration are implemented. More specifically, when a control computer of the engine judges that either a warm-up control (QWS) or a DPD regeneration control has been initiated on the basis of engine water temperature or revolutions and DPD regeneration permitting conditions, the exhaust throttle valve is closed to suppress the exhaust gas flow rate and, as a result, a rise in the exhaust temperature necessary for both accelerating engine warm-up and DPD regeneration is accelerated.
Conventional exhaust throttle valve failure diagnosis has involved the use of a solenoid valve for actuating the exhaust throttle valve, as well as a drive relay for driving the solenoid valve. For example, the control computer executes a circuit diagnosis of the solenoid valve or drive relay electrically connected to the control computer.
However, conventional failure diagnosis such as this has the inherent problem of facilitating only an electrical failure diagnosis and, accordingly, it does not allow for diagnosis of mechanical failure such as that due to close sticking or open sticking of the exhaust throttle valve due to soot or the like.
A concern inherent to an exhaust throttle valve sticking in this way is that it will cause imperfect engine warm-up, power capacity/exhaust gas deterioration due to exhaust resistance, imperfect DPD regeneration, as well as the misdiagnosis of other diagnoses that use air flow rate measurement resulting in erroneous failsafe indications.
Thereupon, the supplementary provision of an opening degree sensor (position sensor) in the exhaust throttle valve to implement a direct diagnosis thereof has been considered as a method for diagnosing the mechanical failure of an exhaust throttle valve.
However, because the exhaust throttle valve constitutes an exhaust system component part there are temperature and vibration-related problems, as well as a cost-related problem inherent thereto, and the supplementary provision of an opening degree sensor and so on thereon involves a mounting step that is difficult to implement. In addition, because the exhaust throttle valve requires no precise opening degree control and is basically ON/OFF controlled, mounting an opening degree sensor for the purpose of diagnosis alone is undesirable from the viewpoint of cost.